Cisco PIX Strange VPN Issue

One of my Clients have a couple of Site to Site Tunnels and now they would like to setup a VPN Client as well. I noticed on the Config that the Client is setup however using RADIUS authentication which to my knowledge is being used. I take out the line:

crypto map outside_map client authentication RADIUS

Some of the Tunnels go down!!

What would cause this to happen even if I issue the correct commands to initate the tunnels. I have never seen this happen before can anyone shed some light on this issue.